1. Field of the Invention
This invention relates to a wind direction and speed indicator, and in particular, to an improved apparatus design that provides greater visibility of the indicator at night and during other low visibility conditions.
2. Description of the Related Art
Airplane pilots who are approaching an airport or landing strip need to know the ground wind direction and relative speed in order to safely land their craft. A number of devices are in use, or have been proposed to assist aviators by indicating wind direction and speed.
Since antiquity, wind vanes have been used for indicating wind direction and some airports continue to use wind vanes for this purpose. For example, the Whitehorse International Airport in Yukon Territory, Canada, has mounted a retired commercial aircraft, a Douglas DC-3, to serve as a wind vane for the airport. Relative wind speed can be indicated with an anemometer, which is believed to have been invented during the Renaissance by Leon Battista Alberti, when he suspended a flat plate from an edge and discovered that the wind would deflect the plate, with the revolutions depending on the wind speed. The anemometer has been updated in more recent times as a cup anemometer, in which the plate is replaced by three or four cups attached by arms to a vertical rod that catch the wind to rotate the rod.
A wind vane and cup anemometer are sometimes positioned on the same vertical rod. Alternatively, another combination of wind vane and anemometer is the aerovane, in which a propeller and a tail are combined on the same horizontal shaft and mounted on a vertical axis for rotation to indicate wind direction.
Perhaps the simplest device for indicating wind direction and relative speed is a windsock, a piece of cloth with a frustoconical shape provided with a rigid circular support for the wider end and mounted for rotation on a vertical shaft. In low winds, the cloth droops, but in higher winds the cloth fills and flies horizontally, indicating the direction in which the wind is blowing. For example, if the windsock is pointing east, that means there is a westerly wind (a wind blowing from west to east). The windsock's angle relative to the ground provides an indication of whether the winds are light, moderate or heavy. Windsocks may be affected by sleet, snow and freezing weather in both their ability to rotate into the wind and also to straighten or extend from a vertical to a horizontal position.
The United States Federal Aviation Authority (FAA) Specification for Wind Cone Assemblies, FAA Advisory Circular 150/5345-27D, requires windsocks to indicate wind direction in winds as light as 3 knots, and to be fully extended in the horizontal position (indicating high winds) at 15 knots. Windsocks may be lighted for nighttime observation, either by floodlights illuminating the exterior of the windsock, or with a pole-mounted light illuminating the windsock's interior.
U.S. Pat. No. 1,879,267, “Wind Indicator for Aviators,” discloses an aerovane in which the casing of the device has a triangular shape with a rudder at the point to steer the aerovane. The casing also contains lamps to provide illumination of the aerovane at night. However, the propeller at the front of the aerovane which provides relative wind speed information is not illuminated. Aviators would therefore have a difficult time gauging wind speed at night.
U.S. Pat. No. 1,911,169, “Air Navigation Apparatus,” discloses a tubular member through which wind passes, as though it were a rigid version of a windsock. The tubular member pivots to indicate the wind direction. Some of the wind passing through the tubular member is diverted and operates a spring and gear mechanism, which controls a pointer that indicates relative wind speed on a large dial mounted on the top of the tubular member. The spring and gear mechanism complicate this device, and the distance at which the dial may be read is not great. In addition, the apparatus is not illuminated for nighttime use.
U.S. Pat. No. 1,953,159, “Means for Indicating the Direction and Velocity of the Wind Near the Ground,” discloses a wind vane with two arms that pivot at different wind speeds, so that a pilot may observe the orientation of the wind vane and the angle of the pivoting arms and determine the wind direction and relative speed. Lights on the vane and arms illuminate for nighttime observation. The design is complicated because of the need to control the pivoting arms.
U.S. Pat. No. 1,969,206, “Device for Giving Luminous Signals, Particularly Adapted for Aviation Purposes,” discloses a wind vane with a projection lamp system that projects the wind direction and speed onto a reflective screen or other surface. This design requires a projection surface, and the reflection of the projected light will not be as visible at a distance as direct illumination would be, especially if the surface were dirty or coated with ice or snow.
U.S. Pat. No. 4,241,604, “Nighttime Wind Direction and Speed Indicator,” discloses a lamp with a rotatable projection lens that concentrates a portion of the light from the lamp and projects it on the nearby ground. The rotatable projection lens is attached to an external wind vane, so that the lens rotates as the wind vane pivots in the wind, with the projected beam indicating wind direction. A cup anemometer on top of the housing is connected to a rotatable shutter internal to the lamp so that the shutter interrupts the projected beam of light, with the frequency of interruption being proportional to the wind speed. It is not clear how an aviator not familiar with the device would relate the flashing to the ground speed of the wind.
U.S. Pat. No. 5,323,649, “Airport Wind Direction and Velocity Indicator,” discloses a housing shaped as a tetrahedron with a triangular cross section that pivots in the wind. The edges of the housing are illuminated, allowing pilots to view the wind direction from a distance at night. In addition, a cup anemometer mounted on the housing measures wind speed, which is projected as large illuminated numerals mounted on the two top sides of the housing.
U.S. Pat. No. 7,310,047, “Gas Alarm System with Wind Direction Indicator,” discloses a mechanism that senses the presence of a hazardous gas and provides annunciation to signal and warn personnel of the hazardous gases and to also alert them as to the direction of the wind carrying the toxic gas.
The devices of the prior art have limited ability for use in regions that may experience conditions of blowing sand and dust at ground level due to complex mechanical systems that could become fouled and that would require frequent inspection and maintenance to assure their continued reliable operation.
Apparatus that display numbers also present problems of deciphering the numerals at a distance as the pilot is approaching the runway or landing strip.
It is therefore an object of the present invention to provide an improved wind speed and direction indicator that is highly visible and readily discernable to the pilot or navigator of an approaching aircraft, particularly under conditions of lowered visibility.
Another object of the invention is to provide such a wind speed and direction indicator that is of robust and durable construction having low maintenance requirements that will remain operable under harsh conditions including, for example, ice, snow, airborne dust and/or sand, and that can be installed at remote airstrips.